1. Field of the Invention
The present invention relates to a process for the formation of a negative resist pattern and also to an apparatus suitable for use in the practice of the process. More specifically, the present invention is concerned with a process for forming a negative resist pattern with a resist containing a diazoquinone sensitizer and also with an image-reversal developing apparatus suitable for use in the practice of the process to perform both reversal of a positive image and development of the reversed, namely, negative image.
2. Description of the Related Art
As has been well-known, a variety of resists, are employed widely in the fabrication of semiconductor devices and the like to form desired patterns on substrates.
These resists include negative resists and positive resists. When imagewise exposed to radiation such as light, electron beams or x-rays, the exposed portion is insolubilized by a developer solution, namely, a solvent, whereby a negative image is provided. On the other hand, a positive resist becomes soluble in such a developer solution at an exposed portion so that a positive pattern is provided. Making use of their respective properties, these resists have found significant utility.
Many of these conventional resists are however used exclusively for the formation of either negative or positive resist patterns. Namely, it is impossible to selectively form either a negative pattern or a positive pattern by using the same resin commonly. Inconveniently, negative resists and positive resists must thus be selectively used depending on whether negative resist patterns are intended or positive resist patterns. Among these resists, positive resists are superior in resolution and the sharpness of printing areas to negative resists. There is hence an outstanding demand for the improvement of the resolution of negative resists.
On the other hand, resists capable of selectively forming either negative or positive patterns by changing treatment conditions in spite of the use of the same sensitizer (photosensitizer), namely, so-called image reversal resists have also been developed.
Among image reversal resists of the above sort, those using as a sensitizer an o-quinonediazide compound (diazoquinone compound; hereinafter called "diazoquinone sensitizer") are mentioned as typical examples.
The reversal of an image formed in a resist, which uses such a diazoquinone sensitizer, is considered to take place in accordance with the following mechanism.
A diazoquinone sensitizer has the characteristic property that upon exposure (first exposure) to radiation, diazo groups are decomposed and at the same time, carboxyl groups are formed. Accordingly, when a positive resist containing such a diazoquinone sensitizer (for example, a resist useful for imagewise exposure through a positive film to form a printing plate bearing a positive pattern) is exposed imagewise to radiation through a positive film by a method known per se in the art, carboxyl groups are formed in the exposed area (i.e., the area corresponding to the image-free area of the positive film), whereby upon treatment with an alkaline developer solution, the exposed area is removed to allow the unexposed area to remain as a pattern, thereby obtaining a positive image.
To obtain a negative image on the other hand, it is necessary to make the resultant carboxyl groups inactive or inert to an alkaline developer solution. To make the area, which is other than that subjected to the first exposure, soluble in an alkali developer solution, after inactivation of the carboxyl groups, full-face exposure (second exposure) is performed, followed by development with an alkaline developer solution. As a result, an image reversed from the aforementioned image, i.e., a negative image is obtained.
A variety of processes has been proposed for the inactivation of carboxyl groups formed by first exposure in a resist which contains a diazoquinone sensitizer, for example, including the process in which a second component capable of promoting decarboxylation of carboxyl groups is added in combination with a diazoquinone sensitizer and heat treatment is applied subsequent to first exposure. Specifically described, it has been proposed to use triethanolamine (see Japanese Patent Application Laid-open No. 127615/1974), a second or tertiary amine (see Japanese Patent Application Laid-Open No. 108002/1975), a 1-hydroxyethyl-2-alkylimidazoline (see Japanese Patent Application Laid-Open No. 6528/1977), a quinone compound or aromatic ketone compound (see Japanese Patent Application Laid-Open No. 127615/1974), a basic carbonium dye (see Japanese Patent Application Laid-Open No. 9740/1981), etc. These conventional reversal processes however require subsequent to first exposure, that a heat treatment be conducted in air, for example, in a constant-temperature air oven maintained around 150.degree. C. for a relatively long period of time, say, 10 minutes or even longer. This constitutes a serious obstacle for practice of these processes. Further, heating in such a constant-temperature air oven locally results in uneven heating. These conventional processes are therefore accompanied by another serious drawback that they cannot provide any pattern of desired quality where the intended pattern is a fine pattern.
A still further process has also been proposed, in which a resist subjected to first exposure is treated with an acidic aqueous solution such as HCl or H.sub.2 SO.sub.4 to decarboxylate carboxyl groups formed by the first exposure (Japanese Patent Application Laid-open No. 3633/1976). This process however requires treatment conditions of a time period as long as 4-5 minutes at a temperature of about 90.degree. C. and involves inevitable corrosion of a treatment apparatus. This process is therefore impractical too.